The present invention relates to a tensioning device for imparting torsional bias to a member such as a shaft and in particular to a tensioning device which will selectively rotationally engage and disengage from the shaft.
The present tensioning device has been found to be particularly useful in connection with conveyor belt cleaners which utilize one or more scraper blades to clean the belt of a Conveyor mechanism. Conveyor belt scraper blades are conventionally mounted on a shaft which is located transverse to the direction of conveyor belt travel. The blades are rotated by the shaft into contact with the belt to scrape off adherent material. Over time the scraper blades wear down and lose contact with the belt thereby hampering the scraper blade's cleaning ability. The shaft on which the scraper blades are mounted must be rotated to reposition the scraper blades against the belt. Various types of tensioning devices have been used in connection with conveyor belt cleaners in order to rotate the shaft and reposition the scraper blades against the belt as the blades wear.
The torsional force for providing rotation of the shaft as the scraper blades wear is typically stored in a resilient torsion coupling member which is twisted about its longitudinal axis. The rotational biasing force stored in the torsional coupling member is typically created by a human operator applying a rotational force to the drive end of the tensioning device with a wrench or other implement in a desired rotational direction. This rotational force applied by the operator is resisted by the engagement of the tips of the scraper blades with the conveyor belt and the underlying head pulley of the conveyor mechanism such that the respective ends of the torsion coupling member twist relative to one another. A serious and potentially injurious problem is encountered when a splice in the conveyor belt or other belt inconsistency or a piece of adherent material being conveyed catches or grabs the tips of the scraper blades and pulls the scraper blades through the gap between the shaft and the conveyor belt thereby providing a large and sudden rotation of the shaft. When such a "pull-through" of the scraper blades occurs, the corresponding rotation of the shaft transmits rotational forces to the drive end of the tensioning device and to the operator thereby potentially causing serious injury to the operator.